screen: Give a default for searchBarOnChange.
screen: Give a default for searchBarOnChange.

This isn't provided by callers which don't use `search`.  A no-op
function is a sensible default even for callers which do, though
perhaps not a very helpful one.

vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile